Power MIS transistors have high breakdown voltage (withstand voltage), high thermal stability and high gain, and can be easily used to realize a construction for power amplification. For this reason, the power MIS transistors are widely used as power devices for switching power sources, motor control power devices, power devices for vehicles or the like, and, in recent years, have been becoming finer and finer to realize far higher performance.
In many cases, to ensure a certain degree of electrostatic breakdown strength, a protection diode (a zener diode) is provided in a semiconductor chip in which a power MIS transistor is formed, and the protection diode is electrically connected between the gate and the source of the power MIS transistor.
In some types of power MIS transistors having built-in protection functions, not only a protection diode but also another protection circuit such as a thermal sense circuit is provided in a semiconductor chip in which a power MIS transistor is formed, and such protection circuit is electrically connected to between the gate and the source of the power MIS transistor.
In general, such power MIS transistor uses a package having a three-terminal structure. In this case, a gate electrode and a source electrode are disposed on a principal surface of the semiconductor chip in which the power MIS transistor is formed, and a drain terminal is disposed on the reverse surface of the semiconductor chip.